In the past, flow meters, connected in-line to a fluid circuit, for measuring the flow rate of a fluid flowing through a channel have been widely adopted. Known examples of such flow meters include meters provided with an orifice, a Venturi nozzle, a pilot tube and the like installed in an appropriate location in the channel and that employ a differential-pressure method in which flow rate is measured from the pressure difference caused by a throttle. Since such a differential-pressure flow meter is used in a region where the fluid usually exhibits turbulent flow, the flow rate becomes large, thus easily causing cavitation.
Since the above-described differential-pressure flow meter has, in addition to the problem of a pressure drop, a problem in that the cost increases to achieve a certain processing accuracy, a flow meter that includes, for example, a pair of probes having slits opening to the channel and that detects the pressure difference of the fluid entering the probes has been proposed. This differential-pressure flow meter is a flow meter that satisfies the principle of dynamic-pressure measurement, has improved measurement accuracy, has a simple structure, and can be manufactured at low cost. (For example, see Patent Document 1.)
Patent Document 1: Japanese Unexamined Patent Application, Publication No. HEI-11-316144